1. Field of the Invention
The invention relates to a hydrocarbon conversion process. The invention specifically relates to the alkylation of hydrocarbons such as aromatics or paraffins to produce useful chemicals and motor fuel. The invention is primarily directed to a process for the solid bed alkylation of isobutane to produce C.sub.8 isoparaffins useful as motor fuel blending components.
2. Related Art
Large amounts of high octane gasoline are produced by the alkylation of isobutane with butenes. Likewise, large amounts of valuable aromatic hydrocarbons including cumene, ethylbenzene and C.sub.16 -C.sub.21 linear alkylaromatics are produced by the alkylation of benzene with olefins of the appropriate carbon number. The variety of feed reactants and the passage of time has led to the development of a number of effective alkylation technologies which are employed in large scale commercial facilities.
One of the most widely used processes for the production of motor fuel is HF alkylation as described in U.S. Pat. No. 4,139,573 issued to D. B. Carson, which provides an overview of the HF alkylation process. One of the advantages of the use of liquid-phase HF as a catalyst is its resistance to deactivation, and the relative ease with which a slipstream may be removed from an onstream reaction zone for "regeneration". The HF itself is not chemically changed during use but various organic reaction by-products such as "acid soluble oils" (ASO) accumulate in the liquid-phase HF and are removed during this regeneration.
Regeneration is also necessary for all solid bed motor fuel alkylation catalysts developed to date since they tend to suffer from a high deactivation rate. Deactivation of solid catalysts is due to different, possibly multiple, causes from those encountered with liquid HF as a catalyst and usually includes some accumulation of hydrocarbonaceous deposits on the catalyst.
A common method of regenerating catalysts is by combustion of organic deposits. This is often not desired for alkylation catalysts. U.S. Pat. No. 3,851,004 to C. L. Yang describes an alternative method for regenerating a solid bed alkylation catalyst comprising a hydrogenation component on a zeolitic support which comprises contacting the catalyst with a hydrogen-containing liquid-phase saturated hydrocarbon.
Any interruption in the operation of the reaction zone to regenerate or replace catalyst is undesirable. Certain operating benefits are provided to any process by an ability to operate in a continuous manner, which makes it desirable to find a means to regenerate or replace the catalyst while the reaction zone is kept in use. U.S. Pat. No. 4,973,780 issued to R. C. Johnson et al describes a moving bed benzene alkylation process in which catalyst is continuously or periodically replaced with regenerated catalyst to provide countercurrent catalyst-reactant flows. Cocurrent flow with catalyst added to the bottom of the reactor is also disclosed.
It has also been proposed to provide continuous operation by simulating the movement of the catalyst through the reaction and regeneration zones. U.S. Pat. Nos. 4,008,291 to R. F. Zabransky et al. and 4,028,430 to L. O. Stine et al. describe the use of simulated countercurrent operations to perform a number of alkylation reactions including the production of motor fuel. These references provide separate reaction and catalyst reactivation zones, with an external regenerant stream being employed for the reactivation. In both references the effluent of the reaction zone is withdrawn from the alkylation zone immediately upon its exit from the reaction zone. These references also teach the use of a "pump around" stream to complete the simulation and provide a continuous liquid loop.
Finally, U.S. Pat. No. 5,157,196 issued to C. S. Crossland et al. describes a moving bed paraffin alkylation process which employs a plug flow in which the catalyst moves upward to a disengaging zone. Used catalyst from the disengaging zone is passed into a wash zone.